Device for aligning contours of fabrics for industrial sewing machines

ABSTRACT

Device for aligning automatically the contours of two plies to be sewed one upon the other, consisting of three superimposed blades (1,2,3) hinged to one another at one end by means of a cross pin (4) so as to generally form a double pliers. From the pin (4) onwards the device comprises :elastic means (7) which can be calibrated and tending to press the blade (2) against the blade (1) and the blade (3) against the blade (2); means (8) to vary the angular opening between the blades (1,2,3), means (9) to adjust the maximum and minimum angular opening between the blades (1,2,3), abuting means (28a,28b,28c) to define the alignment position of the contours of the plies (T,t) to be sewed and means to bring the plies to the alignment on an air pad or by friction.

The present invention relates to a device for the automatic alignment ofthe contours of plies to be conveyed one upon the other to the sewingstation where they are sewed on one another. The device can be also usedto guide only one ply towards the sewing station, for example, when thesewing of an edge, an embroidery or the like has to be made. The deviceaccording to the present invention is designed to have the function ofessential fitting for industrial sewing machines because it producesconsiderable advantages in the sewing industry as far as both thequality of the hand-made goods and the productivity are concerned andalso for the presence of a new aligning system. Some devices andappliances designed to this end are already know. However, theygenerally are integral with mechanic sewing machines which are verycomplicated.

Furthermore they have poor adaptability to the various kind ofprocessing or manufacture and are provided with complicated controlmeans and aligning means which do not assure an optimum result for everykind of goods to be sewed.

The present invention seeks to obviate the above mentionedinconveniences by means of a device that besides being of simpleconstruction and convenient operation assures a better result regardlessof the material characteristics.

Another aim of the present invention is that of providing a deviceoperating as an universal guide which aligns the contours of plies andis applicable to the most dissimilar sewing machines.

The device of the invention is of easy use, not very cumbersome,accurate and designed to be included in and excluded from theprocessing.

The device according to the present invention consists essentially ofthree superimposed, generally rectangular blades which are hinged at oneend and have the form of a double pliers, the three suitably shapedblades engaging in pairs two plies to be sewed together and guiding thecontours thereof so that said contours are parallel and laid one uponthe other. From the end where the hinge pin is places onwards the devicecomprises spring means which can be calibrated and are able to push themiddle blade against the lower blade, and the upper blade against themiddle blade. It is also possible to provide elastic means to oppose theweight of the blades.

The application area of the elastic force pushing the blades towards oneanother is near the hinge axis because the edges of the fabric have totravel almost without friction between the respective pairs of blades.The engaging area of the blades i.e. the operation area of the guides,is formed by the end of the three blades which is opposite to the hingeaxis, said area being provided, as shown later on, with means to makethe alignment easier and being limited by abuting means against whichthe plies to be aligned are beating. In the device, after the abovementioned elastic means a mechanism is provided which is able to opposethe action of said elastic means causing the opening of the blades so asto make the initial insertion of the plies to be aligned and sewedeasier and causing then their closing up to the position of the selectedcalibration which is carried out by means of controlling the maximum andminimum opening angle of the blades under working condition.

The contours of the plies are inserted so that the upper contour entersbetween the upper blade and the middle one, while the lower contourenters between the middle blade and the lower one.

To better intend the features and the advantages of the presentinvention a preferred non-limitative embodiment and some variantsthereof are described with reference to the accompanying drawings,wherein:

FIG. 1 is a top view of the device according to the preferred embodimentof the present invention;

FIG. 1a is the spread out flat view of FIG. 1,

FIG. 2 is the longitudinal section of the device taken along the brokenline A--A of FIG. 1 and showing the device under preliminary conditionbefore the operation;

FIG. 3 is a section similar to the previous one but showing the deviceunder working condition;

FIG. 4 is a partial section in enlarged scale of the means forcontrolling the opening angles between the blades of the device;

FIG. 5 shows in enlarged scale and in greater detail the particular ofthe engaging area and the engaging means of the plies to carry out andmake easier the alignment of the contours shown in FIG. 2;

FIG. 6 is a section similar to that of FIG. 5 but concerning amodification of the engaging means for the alignment of the contours ofthe plies; and

FIGS. 7a and 7b show the sections of the ejecting means.

With reference to the figures, in particular to FIGS. 1 and 2, thedevice for aligning the contours of the plies to be laid one upon theother and sewed together according to a preferred embodimend of theinvention consists of three superimposed generally rectangular blades,the lower blade of which is designated by 1, the middle blade by 2 andthe upper blade by 3. The blades preferably made of a metallic alloy andsuitably shaped are hinged to one another at one end about a transversalpin 4 (FIGS. 2 and 3) and form essentially a double pliers.

The assembly of the three blades 1, 2, 3 of this alignment device ismounted upstream and near the sewing station 5 of an industrial sewingmachine. The assembling can be effected by means of a connecting bracket6 or the like placed at choice on one of the sides of said device. Byway of example reference is made to the bracket 6' of FIG. 1. Thebracket 6, 6' can connect directly the lower blade 1 to the sewingmachine (FIG. 1) or alternatively it can be fastened to the machine byother supporting means allowing the alignment device to be put andmaintained in working conditions or to be put away from the processingby means of a rotation or a translation.

Referring to the FIGS. 1 and 2 and beginning from the hinge pin andproceeding from right to the left-hand side said device comprises:adjustable pressure means generally designated by 7, means for spacingout the blades generally designated by 8, means for controlling theopening angles between the blades generally designated by 9; and finallyabuting and guiding means enabling the contours of the plies to bealigned and sewed together.

The adjustable pressure means 7 are arranged to push independently themiddle blade 2 against the lower blade 1 and the upper blade 3 againstthe middle blade 2.

To this end a vertical, threaded pin 10 is provided which is fastened ina seat formed in the lower blade 1 and passes f through large holesformed in the blades 2 and 3, respectively said large holes allowingsaid pin 10 to freely pass through during the angular motion of theblades 2 and 3 with respect to the blade 1. Two helical springs 11 and12 are coaxially mounted about the pin 10: the spring 11 has a diameterlower than the inner diameter of the spring 12 and has an axial heightsuch as to abut against the middle blade 2 and the lower end of a hollowpin 13 which can be screwed about the pin 10 through its knurled head13a. The hollow pin 13 is threaded also outside so that the threadedring nut 14 can be screwed about it in order to counteract the spring 12which is acting outside the spring 11 in the space defined by the blade3 and the ring nut. In such a position the springs 11 and 12 generate anadjustable load force which is independent in each passage way. Thepiston means 8 allows an adjustable opening of the blades 1, 2, and 2, 3to be obtained in order to enable the initial insertion of the contoursof the plies T and t to be sewed in the guiding means.

From the piston means 8 electrically or pneumatically driven and lockedin place on the upper surface of the plate 3 a piston 15 comes out whenthe piston means is activated and passes through a hole formed in theblade 3 so that is abuts against the head of an abutment pin 17 fastenedat an adjustable height to the lower blade 1. When the piston 15 isretracted the blades 1, 2, 3 are allowed to approach each otheraccording to the respective adjusted positions prefixed by thecontroller 9 under the influence of the return springs 11 and 12.

The means 9 for controlling the opening angles of the blades, which canbe better seen in FIG. 4, has the function of adjusting the angularspacing between the blades 1, 2 and 2, 3 under working conditions andthe maximum angular spacing under preliminary conditions before startingthe operation.

The controlling means 9 comprises: a vertical sleeve means 18 having anupper portion 18a with cylindrical external and internal surface whichare both threaded with a very little pitch and a lower portion 18b withprismatic external surface and cylindrical internal surface. The sleeve18 becomes larger downwards and terminates in an external flange 18clocked in place in a through hole formed in the middle blade 2. At thelower end of the sleeve 18 and at height of the flange 18c recesses areformed in the internal surface for receiving a wire spring 19, thefunction of which is that of pressing the flat surfaces of the prismaticend of a pin 20 which is inside and coaxial to the sleeve 18 in order tohinder the rotation thereof after its micrometric adjustment which canbe carried out according to split turns. The upper portion 20a of thepin 20 is threaded outside with a pitch similar or equal to that of theinside thread of the sleeve 18. The pin 20 terminates at the lower endin a circular head 20c which abuts against a recess 1a formed in theupper surface of the blade 1, so that the adjustment of the angularopening of the blades 1 and 2 can be provided by the rotation of thering nut 21 which is integral with the other end thereof.

About the sleeve means 18 another sleeve 22 is assembled which isthreaded inside and outside and the lower end thereof is widen outforming a flange 23 which is housed in an upper recess 3a axiallyaligned with the hole 25 formed in the upper blade 3 in order to allowthe blades to perfectly adhere to one another. When acting on the ringnut 26 integral with the upper end of the pin 22 the adjustment of theangular opening of the blades 2 and 3 can be provided due to the raisingof the blade 3 with respect to the blade 2. The flange 23 is provided inthe internal surface with recesses simmetrical with respect to thesleeve axis for receiving a wire spring 24 similar to that of the sleeve18 and having the same function.

The external diameter of the flange 23 is then such as not to allow itto pass through the hole 25 which is formed in the upper blade 3 forreceiving the sleeve 22 and is coaxial to the hole 2a receiving thesleeve 18 and formed in the middle blade 2.

A threaded and knurled ring nut 27 establishing the position of themiddle blade 2 with respect to the blades 1 and 3 is mounted about andis freely travelling along the sleeve 22, said ring nut 27 having theexternal diameter larger than that of the hole 25 and engaging byfriction the threaded surface 22a with a ball 27a thrust by a spring 27bsubjected to the action of a screw 27c for calibrating the friction. Itis self evident that the rotation of the knurled nut 21 if the pin 20causes the axial translation of the latter within the sleeve 18 which ismade integral with the middle blade 2 and then when the piston means isnot operating it is possible to adjust the angular opening under workingconditions of the middle blade 2 with respect to the lower blade 1because the pin 20 abuts against the base blade 1. The adjustment can beeffected with high precision due to the very little pitch of the screwthreads and also because it is performed according to split turns of thepin 20 what is possible due to the spring 19 acting on the prismaticportion 20b of the pin 20 which is allowed to rotate only step by step.

In the same way it is possible to adjust the angular opening underworking conditions between the middle blade 2 and the upper blade 2 byacting on the middle knurled ring nut 26 locked in place at the top ofthe sleeve 22. In this case it is the flange 23 that supports the upperblade 3 aising against the action of the spring 12 of the pressure means7 which acts with its spring 11 on the middle blade 2 too.

Also the upper plate 3 is adjusted by split turns of the sleeve 22 dueto the action of the spring 24 that presses the flat surface of theprismatic end 18b of the sleeve 18 in order to adjust the maximumangular opening between the blades 1, 2 and 2, 3, respectively, when thepiston means is operating, i.e. under preliminary conditions, it issufficient to displace the knurled ring nut 27 along the sleeve 22 up tothe desired point. If for example it is assumed that the piston 15 ofthe spacing means 8 comes out slowly, the consequent raising of theupper blade will not cause a displacement of the middle blade till theupper blade 3 comes in touch with the knurled ring nut 27. If the blade3 goes on raising the ring nut 27 trails the middle blade 2 that willdepart progressive away from the base blade 1 up to the end of thestroke of the piston 15 and till reaching the predetermined position.The receiving and aligning areas of the contours of fabrics to bealigned and sewed are formed by the front portions of both innersurfaces of the upper blade 3 and of the lower blade 1, respectively,and of both opposed surfaces of the middle blade 2, as shown in theFIGS. 1, 2, 3, 5 and 6 on the left-hand side of the controller 9. Saidareas are delimited inwardly by three vertical, cylindrical pegs 28a,28b, 28c against which the contours of the plies to be aligned arebeating. Such pegs are fastened to the base blade 1 and pass through theother blades 2 and 3 in openings 29a, 29b, 29c and 29'a, 29'b, 29'cwhich are large enough so as not to hinder the angular displacement ofthe blades 2 and 3 away from the blade 1.

One said pegs 28a, 28b, 28c, if that is the case for further automation,sensors (for example photocells schematically shown dashed in FIG. 3)can be provided which are adapted to sense automatically the presence ofthe plies in the device of the invention. In another embodiment of theinvention besides the assembly of abuting pegs 28a, 28b, 28c alreadydescribed a second assembly of pegs is provided which are fastened tothe blade 2 and are placed parallel to the first assembly. This in orderto provide the offset alignment of the contours. A means is provided tomake easier the travelling of the contours of fabric towards the abutingpegs 28a, 28b, 28c and then the alignment thereof in the area forreceiving and aligning the contours of the plies and in particular onthe upper blade 3 and the lower one 1 near the free ends thereof whichare tapered in order to provide a surface making easier the entry of thefabric plies T and t. According to a first embodiment shown in FIG. 5said means comprises two ejectors able to emit fanlike sprays ofcompressed air which can be oriented, said ejectors being formed byplates 32 locked in their respective seats.

To this end in both upper and lower blades 3 and 1, respectively,cylindrical seats 31b, 31a are provided having frustum-conical sectionstowards the inner surface of the blades. The plates 32a, 32b, are housedin said seats and mate with the frusto-conical section of the seats,thus providing a sealing except for a certain arc, for example 60°, ofthe extension thereof, the shape of the plates providing also a throughhole 34a, 34b which is used as ejector of the compressed air incomingthrough a duct 35a, 35b to the chambers provided under the plates. Theair is supplied by a compressed air source (not shown) through eventualflow controlling valves 36a, 36b (FIG. 1) placed upstream of the ducts35a, 35b. The compressed air provides a swirling jet coming out of theseat and the respective plate tangentially thus forming an air pad inthe desired direction which is able to align the plies. A modificationof the aligning means provides plates 32'a, 32'b having a convex surfaceengaging the ply and identical features as the previous plates as far asthe compressed air ejectors are concerned, such plates being also ableto engage the ply by friction, as described later on.

The operation of the device for aligning the contours of the plies to belaid one upon the other and sewed according to the present invention isas follows:

It is assumed that the device is already installed in the processingline near the sewing station 5, as shown in FIG. 1. The operatoractivates the piston means 8 so that the device can take the positionshown in FIG. 2. By acting on the larger ring nut 27 of the means 9controlling the angular opening of the blades, the most convenientangular openings of the blades are selected to make easier the insertionof the plies T and t, the contours of which have to be laid one upon theother and aligned to be then sewed. The direction of insertion isindicated by the arrows B in FIG. 2, in which T designates a fabric ofhigher thickness and consistency with respect to a second fabric t whichcould be a lining, thus showing how the device of the invention canprocess indifferently materials of different thickness. The piston means8 is then deactivated. This piston 15 returns in its housing 8a in thedirection indicated by the arrow C in FIG. 2 and the blade 2 and 3 arelowered in the direction of the arrow D in order to provide a passageway having a suitable thickness for the material to be sewed. The newposition of the device is shown in FIG. 3. The counteracting springs 11and 12 of the pressure means 7 are suitably adjusted according above allto the maximum thickness of the contours of the plies designed fortravelling between the blades 1, 2, 3, wherein said thickness can dependbesides on the actual consistency of the fabrics also on alreadyexisting folds or seams.

In such a way it is selected the minimum gap which has to be grantedbetween the blades in the receiving and aligning area according to thethickness of the fabrics. The plies T and t of fabrics have to besupplied so as to be able to travel by a greatly reduced friction inorder not to brake too much the action of the feeding equipment of thesewing machine. The gaps between the middle blade 2 and the lower one 1,and between the upper blade 3 and the middle one 2 are selected by meansof the smaller ring nut 21 and the middle one 26 of controller 9,respectively operating as already described and illustrated. When thesuitable gaps are selected the means to make the alignment easier can beactivated and the sewing operation can be started.

If the means to make the alignment easier is the compressed air means,the plates 32a, 32b are suitably oriented so that the action of thecompressed air is tending to bring the contours of the fabric pliesagainst the abuting means 28a, 28b, 28c. The advantage of swinging theplates is that a perfect alignment is provided under different operatingconditions due to the various materials involved. By way of example,when the air jet is directed so as to collide besides with the aligningassembly also with the area of the operator, the unfolding of thefabrics tending to crumple up is provided, and when the air jet isdirected so as to collide besides with the aligning assembly also withthe area opposite to the above mentioned one, a better condition ofcertain kinds of fabric and a certain cooling of the needle of thesewing machine are provided. The compressed air flow regulating valves36a, 36b have to be controlled so as not to cause too strong jets whichcould curl the fabrics.

A further advantage of the present invention is the possibility ofreplacing the flat plates of the present invention with convex plates32'b and 32'a because by the adjustment of the elastic load of thesprings 11 and 12 of the pressure means 7 it is possible to provideengaging areas on the plates causing the plies to be deviated so as tobe directed towards the abuting means, thus providing the alignment. Tothis end the abuting means 28a, 28b, 28c have their axis laying in avertical plane which is inclined by a small angle with respect to thesewing station 5 and to the plane crossing the plane passing through thelongitudinal axis of the means 7 and 9, as shown in FIG. 1.

When the contours of the fabrics to be sewed have gone beyond the deviceof the invention, the already described control operations have to berepeated in order to insert next plies unless the kinds and the featuresof the plies of fabrics remain the same.

It is to be added that even two plies at the time can be passed betweena pair of blades, in this case also the middle blade 2 is provided witha compressed air system making the alignment of the innermost plyeasier. It is also to point out that, when two plies having featuresvery different from each other have to be sewed together, for example asomewhat slippery material between the blades 3 and 2 and a coarsematerial between the blades 2 and 1, both embodiment of the means makingthe alignment easier can be provided in the device of the invention, forexample the compressed air means on the blade 1 and the friction meanson the blade 3.

According to another embodiment of the invention the blades of thedevice can be four so as to sew three plies at the same time.

The device according to the invention illustrated in the figures allowsthe right-hand side of the plies with respect to the operator to bealigned and then sewed. It is self evident that in case of particularrequirement it is possible to provide a device which is specular to thatdescribed herein, i.e. such that alignment of the left-hand side of theplies with respect to the operator is provided. In particular such adevice is shown in FIG. 1a.

I claim:
 1. Device for aligning the contours of two plies for industrialsewing machines, characterized by that it comprises three generallyrectangular shaped blades (1, 2, 3) laid one upon the other and hingedat one end to a transversal hinge pin (4) and arranged like a doublepliers, wherein the lower blade (1) is supported near a sewing station(5) by a connecting bracket (6) to be fastened to a supporting means ofsaid machine between the hinge area of said hinge pin (4) and theopposite end where a receiving area of the plies of fabric (t, T) isprovided, following means being provided after one another from thehinge pin (4) of the blades (1, 2, 3) onwards:return spring means (7) ofthe adjustable type to bring back the blades under working conditionsand to press them against the lower blade (1); means (8) opposing theaction of the return spring means (7) in order to bring the blades (1,2, 3) from the preliminary condition to the working position, thusallowing the insertion of the plies; angular opening controlling means(9) acting on the blades (1, 2, 3) both in the preliminary and workingconditions; abuting means (28a, 28b, 28c) for defining the aligningposition of both plies; and means to make the insertion of the contoursand their alignment easier so that after the adjustment of said meansaccording to the requirements of the plies to be sewed and to theprocessing conditions and after having activated the angular openingmeans and having inserted in the receiving area the contours of theplies to be sewed together, the angular opening means is deactivated andthe aligning means is activated to automatically align the contours ofthe plies to be sewed to each other so that the contour of one ply islaid upon the contour of the second ply and both plies can successivelyreach the sewing station generally parallel to each other.
 2. Deviceaccording to claim 1, wherein said means (7) comprise:(a) a verticalthreaded pin (10) provided with an engaging head (13a) protrudingupwards from the blade (1) and fastened to said blade, (b) a sleeve (13)threaded inside and outside and screwed about the pin (10); (c) a spring(11) surrounding said pin (10), passing through the blade (3) andabutting sleeve (13) and blade (2); (d) a ring nut (14) screwed aboutthe sleeve (13); (e) a spring (12) surrounding spring (11) and abuttingring nut (14) and blade (3), the load of the spring (11) beingadjustable by rotation of the head (13a) of the sleeve (13) and the loadof the spring (12) being adjustable by rotation of the ring nut (14). 3.Device according to claim 1, wherein a piston (15) which preferably ispneumatically driven can come out of the casing (8a) passing through ahole (16) of the blade (3) and presses the head of a vertical pin (17)protruding from the upper surface of the blade (1) and having adjustableheight.
 4. Device according to claim 1, wherein the means (9) for theadjustment of the angular opening of the blade (1, 2, 3) comprise:avertical cylindrical pin (20) which is threaded outside at its upper andmiddle sections (20a) and is prismatic at its lower section (20b), saidpin being widened out at said lower section in a base plate (20c) to beinserted in a seat (1a) opened towards the upper surface of the blade(1), a sleeve (18) which is threaded inside and outside with reducedpitch and is screwed about the pin (20) at the upper and middle section(18a) thereof, said sleeve having a prismatic outside surface andcilindrical inside surface at its lower section (18b) in order toreceive the end (20b) of the pin (20), said sleeve (18) being providedin the lower part with a flange (18c) protruding outwardly anddesignated to be introduced in a complementary seat (2a) formed in theblade (2), and within the flange (18c) diametrally opposed recesses areformed to receive the ends of a spring (19) pressing against theprismatic section (20b) of the pin (20), thus allowing the pin (20) totake on its steady position to effect the adjustment according to splitturns; a sleeve (22) to adjust the maximum raising of the blade (3),said sleeve (22) being threaded outside and being threaded inside onlyat its upper section and screwed about sleeve (18) while it iscylindrical at its lower section, a drive head (26) fastened to theupper part of sleeve 22, a ring nut (27) screwed about said sleeve (22)provided with locking means (27a,27b,27c) for defining the maximumraising of the blade (3) and at its lower end it is widened out in aflange (23) which engages the blade (3) in a recess (3a) thereof, withinsaid flange (23) two recesses being provided which are diametrallyopposed with respect to the axis of the means (9) and are able toconnect the ends of a spring (24) pressing against the prismatic end(18b) of the sleeve (18), thus allowing the sleeve (22) to take on itssteady position to effect the adjustment according to split turns. 5.Device according to claim 1, wherein the abuting means (28a, 28b, 28c)are vertical pegs fastened to the blade (1) and passing through theblades (2 and 3) in holes (29a, 29b, 29 c and 29'a, 29'b, 29'c) saidpegs being generally transversal with respect to the blades (1, 2, 3) inorder to delimitate the insertion area of the contours of the plies,sensing means being able to be secured to said pegs.
 6. Device accordingto claim 1, wherein the means to make the insertion and the alignment ofthe contours of fabrics easier provides two plates (32a, 32b) mounted inseats (31a, 31b) formed in the inner surfaces of the free ends of theblades (1 and 3), said plates being shaped so as to form a periphericslit between each other and their complementary housing seats, undersaid plates a chamber for the incoming compressed air channels (35a and35b) being provided, said channels being connected to a compressed airsource with the interposition of calibrating valves (36a, 36b). 7.Device according to claim 6, wherein the shaped plates (32a and 32b) canbe oriented and adjusted as far as the intensity of the air jet isconcerned and can be replaced with convex plates so as to provide analignment of the ply by the air pad system, or by mechanic frictiondeviation system or both at the same time, the application beingdifferent from blade to blade.
 8. Device according to claim 6, whereinthe outside surface of the plates (32'a, 32'c), which is facing thefabric (T or t), is convex in order to engage by friction the platesover the plies to be aligned.
 9. Device according to claim 1, whereinbesides the assembly of abuting means (28a, 28b, 28c) a second assemblyof abuting means is provided which are secured to the blade (2) and arepassing through the blade (3) and are placed parallel to the firstassembly on the free end side of the blades.
 10. Device according toclaim 1, wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.
 11. Device according to claim 2wherein besides the assembly of abuting means (28a, 28b, 28c) a secondassembly of abuting means is provided which are secured to the blade (2)and are passing through the blade (3) and are placed parallel to thefirst assembly on the free end side of the blades.
 12. Device accordingto claim 2 wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.
 13. Device according to claim 3wherein besides the assembly of abuting means (28a, 28b, 28c) a secondassembly of abuting means is provided which are secured to the blade (2)and are passing through the blade (3) and are placed parallel to thefirst assembly on the free end side of the blades.
 14. Device accordingto claim 3 wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.
 15. Device according to claim 4wherein besides the assembly of abuting means (28a, 28b, 28c) a secondassembly of abuting means is provided which are secured to the blade (2)and are passing through the blade (3) and are placed parallel to thefirst assembly on the free end side of the blades.
 16. Device accordingto claim 4 wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.
 17. Device according to claim 5wherein besides the assembly of abuting means (28a, 28b, 28c) a secondassembly of abuting means is provided which are secured to the blade (2)and are passing through the blade (3) and are placed parallel to thefirst assembly on the free end side of the blades.
 18. Device accordingto claim 5 wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.
 19. Device according to claim 6wherein besides the assembly of abuting means (28a, 28b, 28c) a secondassembly of abuting means is provided which are secured to the blade (2)and are passing through the blade (3) and are placed parallel to thefirst assembly on the free end side of the blades.
 20. Device accordingto claim 6 wherein the middle blade (2) is provided with nozzles forejecting compressed air through it.